(1) Field of the Invention
The present invention relates to a technique of forming on the surface of a metal a coating layer having a thickness of the angstrom order, which is much smaller than the thickness of a layer of a conventional so-called adhesive primer, by applying to the surface of the metal an adhesive molecule capable of being tightly bonded to the metal surface.
(2) Description of the Prior Art
Formation of a strong bonding between a metal and a thermoplastic resin layer is eagerly desired in various fields.
For example, in the field of the can-manufacturing industry, can bodies are often obtained by lapping both the end portions of a metal blank for a can through a thermoplastic adhesive such as a polyamide and heat-bonding the lapped end portions. When the end portions of a metal blank are bonded through a thermoplastic adhesive, the bonding strength between the surface of the metal blank and the thermoplastic adhesive is not sufficiently high and the adhesion tends to be degraded with the lapse of time. As means for solving this problem, there is ordinarily adopted a method in which an adhesive primer such as an epoxy-phenolic resin is coated and baked on a metal material and heat bonding with a thermoplastic resin adhesive is effected through this adhesive primer layer.
However, an epoxy-phenolic lacquer is relatively expensive and the operation of applying this lacquer in the form of a coating layer to the surface of metal material is troublesome. Moreover, since the lacquer has to be applied as a solution in an organic solvent, the solvent cost and the energy cost for baking become increased, and since discharge of the organic solvent in the open air is not allowed, an environmental pollution-preventing equipment such as an after-burner becomes necessary.
Strong bonding between a thermoplastic resin and a metal material is also desired strongly in the field of film-laminated steel plates which are used instead of conventional coated steel plates. Also in this case, the above-mentioned problems similarly arise.